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Postgres Standalone Volume Expansion

This guide will show you how to use KubeDB Ops-manager operator to expand the volume of a Postgres standalone database.

Before You Begin

At first, you need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster.
You must have a StorageClass that supports volume expansion.
Install KubeDB Provisioner and Ops-manager operator in your cluster following the steps here.
You should be familiar with the following KubeDB concepts:

To keep everything isolated, we are going to use a separate namespace called demo throughout this tutorial.

$ kubectl create ns demo
namespace/demo created

Note: YAML files used in this tutorial are stored in docs/guides/postgres/volume-expansion/standalone/yamls directory of kubedb/docs repository.

Expand Volume of Standalone Database

Here, we are going to deploy a Postgres standalone using a supported version by KubeDB operator. Then we are going to apply PostgresOpsRequest to expand its volume.

Prepare Postgres Standalone Database

At first verify that your cluster has a storage class, that supports volume expansion. Let’s check,

$ kubectl get storageclass
NAME                  PROVISIONER               RECLAIMPOLICY   VOLUMEBINDINGMODE   ALLOWVOLUMEEXPANSION   AGE
linode-block-storage  linodebs.csi.linode.com   Delete          Immediate           true                   13m

We can see the output from the linode-block-storage storage class has ALLOWVOLUMEEXPANSION field as true. So, this storage class supports volume expansion. We can use it.

Now, we are going to deploy a Postgres standalone database with version 13.13.

Deploy Postgres standalone

In this section, we are going to deploy a Postgres standalone database with 10GB volume. Then, in the next section we will expand its volume to 12GB using PostgresOpsRequest CRD. Below is the YAML of the Postgres CR that we are going to create,

apiVersion: kubedb.com/v1alpha2
kind: Postgres
metadata:
  name: pg-standalone
  namespace: demo
spec:
  version: "13.13"
  replicas: 1
  standbyMode: Hot
  storageType: Durable
  storage:
    storageClassName: "linode-block-storage"
    accessModes:
      - ReadWriteOnce
    resources:
      requests:
        storage: 10Gi
  terminationPolicy: WipeOut

Let’s create the Postgres CR we have shown above,

$ kubectl create -f https://github.com/kubedb/docs/raw/v2024.6.4/docs/guides/postgres/volume-expansion/standalone/yamls/pg-standalone.yaml
postgres.kubedb.com/pg-standalone created

Now, wait until pg-standalone has status Ready. i.e,

$ kubectl get pg -n demo
NAME            VERSION    STATUS    AGE
pg-standalone   13.13      Ready     3m47s

Let’s check volume size from statefulset, and from the persistent volume,

$ kubectl get sts -n demo pg-standalone -o json | jq '.spec.volumeClaimTemplates[].spec.resources.requests.storage'
"10Gi"

$ kubectl get pv -n demo
NAME                   CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS   CLAIM                       STORAGECLASS          REASON    AGE
pvc-7a8a538d017a4f32   10Gi       RWO            Delete           Bound    demo/data-pg-standalone-0   linode-block-storage  <unset>   7m

You can see the statefulset has 10GB storage, and the capacity of the persistent volume is also 10GB.

We are now ready to apply the PostgresOpsRequest CR to expand the volume of this database.

Volume Expansion

Here, we are going to expand the volume of the standalone database.

Create PostgresOpsRequest

In order to expand the volume of the database, we have to create a PostgresOpsRequest CR with our desired volume size. Below is the YAML of the PostgresOpsRequest CR that we are going to create,

apiVersion: ops.kubedb.com/v1alpha1
kind: PostgresOpsRequest
metadata:
  name: pgops-vol-exp
  namespace: demo
spec:
  apply: IfReady
  databaseRef:
    name: pg-standalone
  type: VolumeExpansion
  volumeExpansion:
    mode: Online
    postgres: 12Gi

Here,

spec.databaseRef.name specifies that we are performing volume expansion operation on pg-stanalone Postgres database.
spec.type specifies that we are performing VolumeExpansion on our database.
spec.volumeExpansion.postgres specifies the desired volume size.
spec.volumeExpansion.mode specifies the desired volume expansion mode(Online or Offline)

Note: If the Storageclass doesn’t support Online volume expansion, Try offline volume expansion by using spec.volumeExpansion.mode:“Offline”.

During Online VolumeExpansion KubeDB expands volume without pausing database object, it directly updates the underlying PVC. And for Offline volume expansion, the database is paused. The Pods are deleted and PVC is updated. Then the database Pods are recreated with updated PVC.

Let’s create the PostgresOpsRequest CR we have shown above,

$ kubectl apply -f https://github.com/kubedb/docs/raw/v2024.6.4/docs/guides/postgres/volume-expansion/standalone/yamls/vol-exp-standalone.yaml
postgresopsrequest.ops.kubedb.com/pgops-vol-exp created

Verify Postgres Standalone volume expanded successfully

If everything goes well, KubeDB Ops-manager operator will update the volume size of Postgres object and related StatefulSet and Persistent Volume.

Let’s wait for PostgresOpsRequest to be Successful. Run the following command to watch PostgresOpsRequest CR,

$ kubectl get postgresopsrequest -n demo
NAME            TYPE              STATUS       AGE
pgops-vol-exp   VolumeExpansion   Successful   10m

We can see from the above output that the PostgresOpsRequest has succeeded. If we describe the PostgresOpsRequest we will get an overview of the steps that were followed to expand the volume of the database.

$ kubectl describe postgresopsrequest pgops-vol-exp -n demo
Name:         pgops-vol-exp
Namespace:    demo
Labels:       <none>
Annotations:  <none>
API Version:  ops.kubedb.com/v1alpha1
Kind:         PostgresOpsRequest
Metadata:
  Creation Timestamp:  2024-03-14T09:04:06Z
  Generation:          1
  Resource Version:    8621
  UID:                 54256467-7bc1-42f5-b0e4-4bf64337b9a0
Spec:
  Apply:  IfReady
  Database Ref:
    Name:  pg-standalone
  Type:    VolumeExpansion
  Volume Expansion:
    Mode:      Online
    Postgres:  12Gi
Status:
  Conditions:
    Last Transition Time:  2024-03-14T09:04:19Z
    Message:               Postgres ops request is expanding volume of database
    Observed Generation:   1
    Reason:                Running
    Status:                True
    Type:                  Running
    Last Transition Time:  2024-03-14T09:05:12Z
    Message:               Online Volume Expansion performed successfully in Postgres pods for PostgresDBOpsRequest: demo/pgops-vol-exp
    Observed Generation:   1
    Reason:                VolumeExpansion
    Status:                True
    Type:                  VolumeExpansion
    Last Transition Time:  2024-03-14T09:06:08Z
    Message:               StatefulSet is recreated
    Observed Generation:   1
    Reason:                ReadyStatefulSets
    Status:                True
    Type:                  ReadyStatefulSets
    Last Transition Time:  2024-03-14T09:06:52Z
    Message:               Successfully Expanded Volume.
    Observed Generation:   1
    Reason:                Successful
    Status:                True
    Type:                  Successful
  Observed Generation:     1
  Phase:                   Successful
Events:
  Type    Reason             Age   From                         Message
  ----    ------             ----  ----                         -------
  Normal  PauseDatabase      12m   KubeDB Ops-manager Operator  Pausing Postgres demo/pg-standalone
  Normal  PauseDatabase      12m   KubeDB Ops-manager Operator  Successfully paused Postgres demo/pg-standalone
  Normal  VolumeExpansion    11m   KubeDB Ops-manager Operator  Online Volume Expansion performed successfully in Postgres pods for PostgresDBOpsRequest: demo/pgops-vol-exp
  Normal  ResumeDatabase     11m   KubeDB Ops-manager Operator  Resuming PostgreSQL demo/pg-standalone
  Normal  ResumeDatabase     11m   KubeDB Ops-manager Operator  Successfully resumed PostgreSQL demo/pg-standalone
  Normal  PauseDatabase      11m   KubeDB Ops-manager Operator  Pausing Postgres demo/pg-standalone
  Normal  PauseDatabase      11m   KubeDB Ops-manager Operator  Successfully paused Postgres demo/pg-standalone
  Normal  ReadyStatefulSets  10m   KubeDB Ops-manager Operator  StatefulSet is recreated
  Normal  Successful         10m   KubeDB Ops-manager Operator  Successfully Expanded Volume

Now, we are going to verify from the Statefulset, and the Persistent Volume whether the volume of the standalone database has expanded to meet the desired state, Let’s check,

$ kubectl get sts -n demo pg-standalone -o json | jq '.spec.volumeClaimTemplates[].spec.resources.requests.storage'
"12Gi"

$ kubectl get pv -n demo
NAME                   CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS   CLAIM                       STORAGECLASS           REASON   AGE
pvc-7a8a538d017a4f32   12Gi       RWO            Delete           Bound    demo/data-pg-standalone-0   linode-block-storage   <unset>  3m8s

The above output verifies that we have successfully expanded the volume of the Postgres standalone database.

Cleaning Up

To clean up the Kubernetes resources created by this tutorial, run:

$ kubectl delete pg -n demo pg-standalone
postgres.kubedb.com "pg-standalone" deleted

$ kubectl delete postgresopsrequest -n demo pgops-vol-exp
postgresopsrequest.ops.kubedb.com "pgops-vol-exp" deleted

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